1. Field of the Invention
The present invention relates to a manufacturing method for manufacturing a semiconductor device and, more particularly, a manufacturing method for manufacturing a semiconductor device, which is suitably applied to an IGBT, DMOSFET or the like.
2. Description of the Related Art
Among MOS type semiconductor devices such as an IGBT or DMOSFET, there is one which has a groove in the surface of its semiconductor substrate. In this type of semiconductor device, a gate electrode is disposed on the groove through a gate insulation film and a channel region is formed in the semiconductor substrate along the side surface of the groove. As a manufacturing method for manufacturing the semiconductor device having this groove structure, see U.S. Pat. No. 5,470,770, a mask which has been patterned to a predetermined shape is disposed on a silicon substrate, and, through the openings of the mask, chemical dry etching is performed to thereby form a groove. Then, within this groove, a LOCOS (Local Oxidation of Silicon) oxide film is formed. Further, by removing the LOCOS oxide film, the groove is completed and then a gate electrode is disposed in the groove through a gate oxide film.
It is to be noted that the word "groove" which is used in this specification represents not only an elongate groove but also a short groove (e.g., one which is square shaped when viewed from above).
However, in this manufacturing method, after the chemical dry etching is performed, an angular portion which is defined between the side surface of the groove and the upper surface of the substrate inconveniently sharpens, raising the problem that the electric field is concentrated on this angular portion. As a result, the service life of the gate becomes varied or short. That is, the end of the LOCOS oxide film which corresponds to this angular portion becomes a "bird's beak", and so the degree in which the angular portion sharpens does not almost become low even after the formation of the gate oxide film. For this reason, the concentration of the electric field occurs.